Go to the signature that you want to work on and for this example we are working in adding Microsoft Teams to their Mobile Phone Field:
1st Step is to Highlight the Field that you want to add in the link to Microsoft Teams.
2nd Step is to click on the Link Icon as shown below:
3rd Step is to click the Link Info tab then select the Link Type as URL, Protocol should be selected as <other> and in the URL field type in sip:((Email))
sip:((Email))Click OK to save, to finalize all the revisions click OK again.
Once saved, and when Recipients of the email clicks on the edited Field it will provide them an option to which program to use.